Articulated aerial ladder



May 17, 1960 L ARTICULATED AERIAL LADDER 4 Sheets-Sheet 1 Filed April15. 1955 INVENTOR. T]? orncz s R. Ha J] May 17, 1960 T. R. HALL2,936,848

ARTICULATED AERIAL LADDER 4 sheets sheet 2 Filed April 15. 1955 May 17,1960 T. HALL 2,936,343

ARTICULATED AERIAL LADDER Filed April 15. 1955 4 Sheets-Sheet 3 N 6 00 Nn IN VEN TOR.

ghoma s R. Ha I] y 1960 T. R. HALL 2,936,848

ARTICULATED AERIAL LADDER 4 Sheets-Sheet 4 UP MASTER OUT .1. LEFT DOWNIN RIGHT .L .1 .1 .1.

Filld April 15. 1955 INVENTOR.

Y gvomczs filial] United States Patent ARTICULATED AERIAL LADDER ThomasR. Hall, Portland, 0reg., assignor, by mesne assignments, toMcCabe-Powers Body Company, a corporation of California ApplicationApril 15, 1955, SerialNo. 501,554

12 Claims. (Cl. 18246) This invention relates to a truck mounted aerialladder useful to utility crews for street light maintenance, generalline work, and tree trimming.

One object of my invention is to provide an aerial ladder of moderatecost utilizing a laminar construction of woven glass cloth and glassfiber matting with a thermosetting polyester casting resin as a binderso as to yield a ladder of high electrical insulating value, long life,and superior structural strength.

Another object of my invention is to provide the terminal end of amovable, powered aerial ladder with a work platform having electricalcontrols so a workman standing upon the platform selectively may causethe ladder to move in any of three degrees of movement, up or down, inor out, and to and fro. A correlated objective is the provision ofladder side rails which protect and insulate the electric cable whichleads to the above mentioned platform controls from the base of theladder.

The aerial ladder of the instant invention is particu-' larly adaptedfor use by utility maintenance crews in work upon street lights,electric and telephone transmission lines, tree trimming operations, andthe like. The ladder itself is mounted upon a truck chassis and isarticulated and powered so as to provide three degrees of movement. Theend of the extensible section of the ladder may reach 35 feet or moreabove the truck chassis. This end carries a novel three section workplatform upon which a workman can stand while he Works. In addition,electric foot control switches are located upon the outermost edge ofthe work platform sections for actuation by one foot of the workmanwhile he stands with the other foot upon a level surface. In accord withone object of my invention, the extensible section of the ladder whichcarries the platform is built up in a mold and cured to provide alaminar construction of woven glass cloth and glass fiber matting with athermosetting polyester casting resin as a binder. This is an effectiveinsulating material which thus isolates the workmen from the ground andserves as a protection should the ladder or platform inadvertently comeinto contact with a high voltage line. As an additional safety factor,the work platform is bounded on the side by a pair of looped hand rails.With or without a safety belt, the workman thus can free his hands torepair telephone, power, or light wires, trim trees, or service streetlights while located 35 feet or more above the street level. At the sametime, his fellow workman can climb the ladder should additional tools orthe like he needed on the job.

The primary requisites for anaerial ladder of the type above described,include safety devices to protect the workman, adequate insulation,structural strength, mobility and an actuation mechanism which istrouble free yet inexpensive. These requirements have been satisfied inthe instant invention with structures which are an improvement uponprior aerial ladders and which form the subject matter of my inventiveobjects. Firstly, the ladder itself is formed with a lower sectionmounted upon a base or stand and an upper section which is 2,936,848Patented May 17, 1960 formed of insulating material and is extensiblewith respect to the lower section. In fabricating the insulated uppersection, a wood center core is completely encased in a glass and plasticcoating having a high tensile strength. At the same time, a flange isformed of the same glass and plastic material so as to define a stringeror side rail for the ladder having the approximate form of a structuralsteel bulb bar member. Utilizing a pair of these high tensile strengthstringers, I can support more than 750 pounds of weight at the end of aladder having an overall length of 35 feet without employing anysupplementary truss or cable reinforcing members. At the same time, astringer formed in this manner is impervious to moisture and weather, ispossessed of an almost indefinite useful life, and the material itselfexhibits exceptionally good electrical insulation qualities.

As another feature of my invention, the truck mounted base of the laddercarries electric actuation means which are operable from the battery ofthe truck itself. These electric actuation means are operable from theWork platform through an electric cable which interconnects the base andterminal end by novel structure. This novel structure takes the form ofa hollow longitudinal tunnel which pierces one of the side railstringers 0f the ladder. The electric control cable to interconnect thecontrol means on the work platform and electric actuated means adjacentthe base is carried in this tunnel. Thus, the cable is protected fromwear and from inadvertent contact with the high voltage lines aboutwhich the ladder may be worked. The provision of this structure is oneobject of my invention.

Another feature of my invention resides in the provision of a hightensile strength in a ladder side rail of minimal overall size. Thisstrength is provided by plural layers of woven glass cloth encased inthe flange of each side rail stringer such that the glass cloth iscontinuous the full length of the side rail. The cloth is held in placeby the use of a casting resin so as to provide a high tensile strengthand the provision of this structure is another of my inventive objects.

Another of my inventive objects is to provide an articulated aerialladder with electric actuation means which are operable from the batteryof the truck upon which the ladder is mounted in order that the laddercan be installed at minimal cost upon existing trucks.

These and other objects and advantages of my invention will becomeapparent during consideration of the following detailed description,taken in conjunction with the accompanying drawings, wherein:

' Fig. l is a perspective view of the aerial ladder mounted upon a truckand partially extended therefrom with a workman standing upon the threesection platform;

Fig. 2 is a foreshortened side View of the ladder with the outer railremoved to reveal the operating elements of the extensible innersection;

Fig. 3 is a detail view of the upper end of both sections of the ladderwith the work platform shown retracted for storage or transportation;

Figs. 4 and 5 are related" rear and side views of the pedestal or standupon which the lower end of the ladder is mounted to provide threedegrees of movement;

Fig. 6 is a broken detail view, taken substantially on the line 6--6 ofFig. 4, showing the details of the journaled housing which allows theladder to be rotated about a vertical axis;

Fig. 7 is a detail view also partially broken away, taken substantiallyon the line 7-7 of Fig. 5, showingthe hydraulic piston and cylindermotor which pivots the ladder up and down about a horizontal axis;

Fig. 8 is an enlarged detail view, taken substantially on the line 8-8of Fig. 3, showing the relative positions of the upper and lower ladderelements during use;

Fig. 9 is a detail view, taken substantially on the line 9-9 of Fig. 8,showing one of the rungs of the ladder and the manner in which boltshold that rung to the side rails;

Fig. 10 is an enlarged detail view in cross section showing one of theside rail stringers and more particularly indicating the laminarconstruction which encases the wood core and forms the flange; and

Fig. 11 is a schematic diagram showing both the electric and hydraulicelements which control the three degrees of movement of the ladder,certain of these elements being indicated diagrammatically by theirconventional symbols.

The ladder illustrated in the drawings is shown mounted upon a utilitytruck 15 having a cab over frame 16 upon which the ladder rests whilebeing transported from place to place. The ladder itself consists of alower metal section 17 and an upper plastic, glass and wood section 18.A work platform 19 is mounted adjacent the terminal end of the uppersection. In addition, the lower end of the section 17 is mounted upon astand or base (illustrated in Figs. 4 and and the upper section ismounted for extension and retraction with respect to the lower section.The aforementioned three degrees of movement are provided (up or down,in or out, and to and fro) so as to adapt the ladder for street lightmaintenance, general line work, and tree trimming operations. In many ofthese uses, it is essential that the workmen standing upon the platform19 be electrically. insulated from the ground so that inadvertentcontact with high voltage lines will do no harm. To this end, the upperladder section 18 is formed of a material of high electrical insulatingvalue as now will be described.

Referring particularly to Figs. 8 and 10, the upper section of theladder includes a pair of elongated parallel stringers 20 and 21. Thesedefine the side rails of the upper section and a plurality of parallellateral tubular metal rungs 22 are carried therebetween. Each of thestringers or side rails is of a laminar construction of woven glasscloth and glass fiber matting with a thermosetting polyester castingresin as a binder. This material is possessed of high insulating valueas well as a high tensile strength and the casting of an exemplarystringer side rail will be described in detail.

To the above end, it will be noted that each stringer has the form of abulb bar structural member with the bulb portion 23 being rectangular incross section and the flange portion 24 which extends the length of thestringer, being a flat plane extension of one long side of therectangle. To lay up a stringer, I employ a cavity mold of the sameconfiguration as the finished side rail illustrated in Fig. 10. Thewoven glass cloth is available commercially as a continuous long pieceof material. A single layer of this cloth is placed in the bottom of thecavity of the mold and a layer of glass matting is placed thereover withthe ends of both the cloth and matting draped over the outside of themold. The

matting itself is two inch long fibers of glass which are positioned inthe mold on shoulders which hold it inplace.

In detail, the wood center core 25 consists of two separate halves whichare elongated pieces of wood arranged to abut and fit together along thelongitudinal center line of the finished bulb portion 23. An ordinarytwo by four which has been split lengthwise will serve this purpose. Inaddition, the core of at least one of the stringer side rails shouldcontain a hollow longitudinal tunnel 26 which extends end to end. Eachsuch tunnel (only one is illustrated) defines a cable way for anelectric cable and/or an air hose. To form this hollow tunnel, asemicircular recess is rabbeted lengthwise in each half of the corebefore the wood pieces are fitted together.

After positioning the wood in the cavity of the bulb, a second layer ofglass cloth and glass matting is cut to size and is placed over the woodand along the flange. Lastly, the remaining excess lengths of glasscloth and matting from the first layer in the mold are folded across thetop of the wood and flange portions of the mold to define a fifth andsixth layer. In final effect, this provides six separate layers (threeof glass cloth and three of glass matting) which extend lengthwise theentire length of the stringer. From bottom to top in the mold, theselayers are one of cloth, matting, cloth, matting, matting, and cloth.With all of these layers in place, the material is impregnatedthoroughly with the polyester resin. The mass then is cured for fourhours with a top or lid over the mold. Upon removal from the mold, theside rail is ready for use in the aerial ladder. By actual test, I havefound that the woven glass cloth which extends lengthwise along theflange adds sufiicient tensile strength to the stringer to support thework platform 19 and a worker with a large margin of safety. At the sametime, these laminar plastic and glass side rails are exceptionally goodinsulators and are substantially impervious to moisture and weather.Even under conditions of severe usage for a long period of time theywill wear well and maintain their strength.

In assembling the upper section 18 of the ladder, two of the side railsand a plurality of the metal rungs 22 are provided. At equispacedpoints, the side rails are drilled so as to accommodate flush fittingbolts 27 to secure the rungs in place and, at the same time, to exert alateral compressive squeeze upon the rails. Lengthwise, of course, therungs 22 are spaced from one another thereby preserving the insulatingqualities of the upper section. Further, the work platform 19 is pivotedadjacent the outer terminal end of this upper section as shown at 28 inFig. 3 so as to allow adjustment and retraction movements. The platformitself includes three flat floor sections. The inner section isidentified by the reference numeral 29, the intermediate section by thereference numeral 30, and the outer section by the reference numeral 31.Two chains 32 interconnect the outer section 31 with selected ones ofthe eyes 33 to provide an adjustment for the final position of theplatform with respect to the ladder. Finally, a plurality of electricfoot control switches 34 and a pair of looped safety rails 35 are addedto the platform structure.

In use, a workman stands upon an appropriate one of the floor sectionsof the work platform as shown in Fig. 1 and either grasps the safetyrail 35 or secures his safety belt to the loops provided on the innerside of this safety rail. In either event, his hands are free to workand a control of the movements of the ladder can be effected by amanipulation of the control switches 34 in a manner hereinafter to bedescribed. At the same time, the worker is protected against fallingforward by the lateral brace members 36 which join the looped safetyrails 35. Several advantages flow from the use of this structure. Firstof all, the three fiat floor sections allow the worker to stand onsubstantially a level fioor section in any elevated position of theladder. For example, in a lower position the worker will stand upon theouter section 31. With the ladder at an angle of approximately fortyfive degrees, the intermediate section 30 will be employed. Similarly,when the ladder is substantially vertical, the inner fiat section 29will be utilized to stand upon. Other intermediate adjustments can beeffected by changing the position of the chains 32 in the eyes 33. In

some instances, the workman will stand with one foot upon. onesectionand the other foot upon another section to brace himself. In thisconnection, it. will be noted that the adjoining sections of the floorof the platform subtend an angle of less than 180 degrees. Thisprovides, at all times, a substantially level section, a brace for thefeet, and a telltale or an indicia for the position of the worker uponthe platform. Independently of the safety rails 35 and 36, the workerwill realize that he should not step beyond the third fiat section.Knowing which section he is standing upon, he thus will be protectedagainst inadvertently stepping off of the platform. Another advantagewhich occurs to the use of this flat surfaced platform is that it ismore comfortable for a worker to'stand upon a flat surface than upon acurved or a l'adder'like structure made up of rungs. For this reason, Iform each of the flat floor sections of. expanded metal or the like.This provides a continuous nonslip surface for the shoes of the worker.

Referring now to Figs. 2, 3, and 8, it will be seen that the lowerladder section preferably is a pair of trusses formed of metal and eachincluding a channel section 37. The legs of the channel members straddlethe bulb portion 23 of the upper side rails to serve as a guide duringextension and retraction of the ladder. In addition, each of the siderails of the lower ladder section is reinforced with a structure 38having two pairs of journaled wheels 39 adjacent the upper end thereof.As best shown in Figs. 3 and 8, the periphery of these wheels projectwithin the outline bounded by the legs of the channels 37 as the upperand lower surfaces of the side rails roll thereupon. One pair of wheels39- is positioned adjacent the lower surface of the side rails and asecond pair adjacent the upper surface to allow the upper ladder sectionto slide smoothly during extension and retraction.

Turning now to Figs. 4 to 7 inclusive, the lower ladder section 17 ispivoted on a lateral bar or pivot member 40. The ladder thus can swingup and down as required. In addition, a hydraulic piston and cylindermotor 41 is secured at its lower end to a base member 42 and, at itsupper end, to the truss structure 38 of the lower ladder section. As isevident in the broken sections of Fig. 7, a supply of hydraulice fluidto this motor unit 41 will raise the ladder by pivoting the same aboutthe pivot bar 40. Similarly, when hydraulic pressure fluid is exhaustedfrom this motor unit 41, the weight of the ladder allows the same to belowered.

Means are provided in conjunction with the apparatus for raising theladder to stabilize the ladder against lateral twisting. Referringparticularly to Fig. '7, the motor 41 comprises a cylinder 60 pivotallyconnected by means of brackets 62 and a pin 63 to the lower end of thebase member 42 the axis of the pin 63 being parallel to the axis of thepivot member 40. Mounted in the cylinder 60 is a piston 64 which extendsoutwardly of the upper end of the cylinder 60. Mounted exteriorly of thecylinder 69 is an elongate guide tube or rigid sleeve 65 which isslidable lengthwise of the cylinder. Extending between and journaled tothe opposite truss structures 38 of the lower ladder section is a crossbar 66, the cross bar being parallel to the pivot member 40. and beingspaced outwardly along the ladder section 17 with respect to the pivotmember 40. The sleeve 65 and piston 64 are each rigidly secured at theirupper ends to the cross bar 66. Thus, actuation of the motor 41 andextension of the piston 64 will effect pivoting of the ladder about thepivot member 49, the guide sleeve moving simultaneously upwardly alongthe cylinder 60 with the piston 64. Engaging the cross bar 66 adjacentthe truss structure 38 of the oppositestringers are struts 67 whichextend from the cross bar 66 angularly inwardly toward the lower end ofthe sleeve 65 and to which they are fixedly secured. A pair of bracemembers 68 may also be provided between each of the struts 67 and thesleeve 65fa'djacent the upper 'end of the latter soas to assist inretaining the'correcponding ends of the struts in fixed "relationrelative to the sleeve. As will be apparent withreference to Fig. 7, anytwisting of the ladder will be resisted by the struts 67 and thevertical component of any twisting force will be translated by thestruts to a horizontal component against the motor cylinder 60. Sincethe cylinder 60 is fixed, twisting of the ladder will be prevented.

As will be seen by reference to Fig. 5, the axes of the pin 63 and thecross bar 66 are parallel to each other and are, in turn, parallel tothe main pivot member 40. In fact, the pin 63, the cross bar 66, and themain pivot member 40 are all carried by the base member 42, which is, inturn, rotatably mounted upon the fixed standard 43', as shown in Fig. 6.Thus, the parallel relationship between the pin 63, the cross bar 66,and the main pivot member 40, is preserved at all times.

To revolve or swing the ladder about the fixed. standard 43, the basemember 42 is joined thereon as shown in Fig. 6. In cooperationtherewith, an electric motor 44 is connected by appropriate chain andsprocket mechanism to a worm which engages a worm follower carried bythe periphery of the fixed standard 43. This rotation mechanism isconventional and the details thereof will not be described except topoint out that actuation of the electric motor 44 in one direction willswing the entire ladder about a vertical axis in one direction and anactuation of the electric motor for an opposite rotation will swing theladder oppositely. Further, by utilizing an electric starter motor 44, Iam able to operate the motor directly from the battery of the vehicle15.

To extend and to retract the upper section 18 with respect to the lowersection 17, I mount an elongated chain 45 adjacent each side of theladder. These chains are reeved about appropriate sprockets and anelectric motor drive 46 (see Fig. 11) is geared thereto. The lower endsof the upper section of the ladder are joined with bolts and metalplates to appropriate sections of these chains such that a rotation ofthe electric motor 46 in one direction will extend the ladder and areverse rotation will retract the ladder. Further, in similarity withthe electric motor 44, I prefer to utilize an electric starter motorwhich also can be operated from the vehicle battery represented by thenumeral 47 in Fig. 11.

Referring now to the schematic diagram of Fig. ll, it will be seen thattwo sets of electric control switches are provided for the aerialladder. The upper set of these control switches is a diagrammaticrepresentation of the foot control switches 34 shown upon the platform19. The lower set of these switches fits upon the base member 42 foraccess by a worker standing upon the bed of the truck should thisoptional method of actuation be desired. As shown in the schematicdiagram, a pluraiity' of electric wires interconnect these two sets ofswitches and the various electric motors which control the three degreesof movement of the ladder. These electric wires are gathered together ina single cable which is identified by the reference numeral 48. It isthis same cable 48 which traverses the aforementioned hollow tunnel 26within one of the side rails of the upper section. To maintain aconstant tension in this cable while the ladder is extended andretracted, I reeve an intermediate portion thereof about a pulley wheel49 and lay the remainder down along the length of the upper laddersection to a point where it enters the lower end of the hollow tunnel26. The pulley wheel 49, in turn, is strapped to a second pulley wheel50 having a tension cable 51 reeved thereabout. One end of this tensioncable 51 is secured to the upper ladder section and the opposite end tothe lower ladder section. In this manner, an extension of the upperladder section carries with it the end of the cable 51 thereby drawingthe pulleys 49 and 50 upwardly and maintaining the constant tension inthe control cable 48.

Referring again to Fig. 11, the various electrical and hydraulicelements are represented diagrammatically to illustrate their function.Each of the electric switches is spring biased to an open position andbears an identifying name related to the corresponding function which iseffected by a closure thereof. For example, closure of the switchlabeled left will swing the entire ladder to the left through anactuation of the solenoid L and an appropriate energization of theelectric motor 44. The master switch, on the other hand, controls thehold solenoid M. This acts as a master cutofi which opens the entireelectric circuit upon deenergization of the sole noid M. After themaster switch once has been depressed, a manual reset thereof isrequired as a safety feature.

To supply pressure fluid to and from the aforementioned hydraulic pistonand cylinder motor 41, I provide two pumps 52 which derive hydraulicfluid from a reservoir 53 and are joined to the motor by a conduit 54. Apair of electric motors 55 actuate the pumps 52 through a singleappropriate solenoid identified by the reference letter U. To lower theladder, on the other hand, a solenoid valve D in a bypass line isactuated through depression of the control button labeled down. Sincethe operation of most of these elements will be apparent, a detaileddescription will not be effected. Instead, the various functions willbecome apparent during a description of a typical use to which theaerial ladder is put.

In the operation of the aerial ladder, it will be assumed that thevehicle 15 has been located adjacent the base of a pole which supportshigh tension electric wires to which repairs must be made. Duringtransportation, the ladder is retracted to rest upon the frame 16thereby automatically pivoting the platform 19 to the position of Fig. 3when the inner flat section 29 contacts a cross member on the lowersection. To effect the required repair to the high tension lines, theworkman can climb the ladder and stand upon the work platform 19 eitherbefore or after that platform is positioned adjacent the point ofrepair. In either event, an appropriate manipulation of either set ofcontrols will move the ladder. For example, depression of the footcontrol switches 34 will manipulate the ladder in three degrees ofmovement to the desired position. To extend the ladder, the on pushbutton is depressed. This will energize the relay causing the electricmotor 46 to rotate the chain 45 upon its sprockets. Rotation of thischain carries the upper ladder section outwardly until either theelectric switch is opened or the parts reach their limit of travelthrough mechanical abutment.

In similar manner, the ladder can be swung to the right or to the leftand can be pivoted up and down about the pivot rod 40. The latter typeof movement, of course, is effected through the electric motors 55 andthe pumps 52 to actuate the hydraulic piston and cylinder motor 41. Oncein position, the desired repairs can be effected without fear ofinadvertent contact of the ladder with the high voltage lines since theupper section 18 is an insulated entity. Further, the electric controlcable 48 is protected within the coating or sheathing of plastic andglass which surrounds the core of the side rails 20 and 21. The workmanis protected against falling by the safety rails 35 and 36 and, wheredesired, he can hook his safety belt to the loops shown carried by theinner portion of the rails 35. While standing upon the platform 19, theworker can manipulate the foot control switches 34 without fear ofslipping since the floor of the platform is flat and continuous asillustrated. Should the ladder be raised or lowered with the workmanthereon, he will step from section to section thereby maintaining anapproximately level position at all times. During an actual movement, ofcourse, he can brace himself by placing one foot on each of twoadjoining sections.

In accordance with the objects of my invention, it will be seen that Ihave provided an inexpensive aerial ladder which is of superiorstructural strength yet of minimal size, This ladder is ,capable ofthree degrees of movement with complete safety to the worker. Further,this priate vehicle since the electric motors can be actuated from thebattery which is carried by such vehicles. In use, the combinationplastic and glass ladder section is an insulator, is extremely durable,and is weather resistant. In addition, it has a high tensile strengthwithout a massive or complex truss and will not bend because of theglass cloth which is incorporated in the flange of the side rails.

I claim:

1. In combination, a ladder havin electric actuation means mountedadjacent the lower end of said ladder and operable selectively to movethe ladder in any of three degrees of movement up or down, in or out andto or fro, a work platform carried adjacent the terminal end of saidladder, and electric control means mounted upon said platform for theselective control from the platform of said electric actuation means,said ladder having two elongated side rail stringers one of which ispierced by a hollow longitudinal tunnel in which is carried an electriccable interconnecting said electric actuation and control means, saidwork platform including an inner, an intermediate and an outercontinuous flat floor section joined end to end with adjoining sectionssubtendin an angle of less than degrees, said inner floor section beingjournaled upon said ladder and cooperating with adjustable suspensionmeans interconnecting the outer floor section and the ladder to positionthe platform with respect to the ladder, said electric control meansincluding a plurality of foot control switchesarranged adjacent theouter edge of said outer floor section for actuation by the foot of aworkman standing upon the work platform.

2. A ladder, comprising lower and upper ladder sections extensible withrespect to one another, a pair of elongated parallel stringers definingthe side rails of said upper sections, each of said stringers having theform of a bulb bar structural member having a cross sectional shapeconsisting of a rectangle and an outwardly projecting flangesubstantially narrower in thickness than the thickness of the rectangle,said flange being substantially an extension of one side face of therectangle, said lower ladder section including a pair of elongated metaltruss structures defining the lower section side rails and in which saidupper section side rails slidably are mounted, and each said uppersection stringer having a center core completely encased in a glass andplastic coating to yield a stringer of high electrical insulating value.

3. An aerial ladder, comprising a lower ladder section carrying an upperladder section which is extensible with respect thereto, said uppersection including a pair of elongated parallel stringers defining siderails and carrying a plurality of parallel lateral rungs therebetween,each of said stringers having the form of a bulb bar structural memberwith the bulb portion being rectangular in cross section and the flangeportion being a fiat plane extension of one side of the bulb portion,said lower ladder section including a pair of side rails each of whichcomprises an elongated metal channel section in which one of said uppersection stringers is mounted, said upper section bulb portions beingguided for extension movement upon journaled roller wheels which arecarried by said lower section channels and which project within theoutline bounded by the legs of the channels, and each said bulb portionhaving a wood center core completely encased in a built up glass andplastic coating and each said flange portion being formed of the builtup glass and plastic per se to yield a stringer of high electricalinsulating value, said upper section lateral rungs being spaced andtherefore insulated one from another.

4. An insulated extensible section for an aerial ladder, comprising apair of elongated parallel stringers defining side rails and carrying aplurality of parallel lateral rungs therebetween, each of said stringershaving the form of 8 bulb bar structural memberwith the bulb portionbeing rectangular in cross section andthe flange portion being a flatplane extension of one long side of the bulb portion, said flangeportion being substantially thinner in the transverse direction than thedimension of the rectangular bulb portion in its transverse dimension,each said bulb portion having a center core completely encased in aplastic coating and each said flange portion being formed of the builtup laminar construction with glass and plastic materials to'yield astringer of high electrical insulating value and high mechanicalstrength, said lateral rungs being spaced and therefore electricallyinsulated one from another and being secured to said side rails by boltmeans passing through and exerting a lateral compressive force upon saidbulb portions.

5. An extensible section for a bladder, comprising a pair of elongatedparallel stringers each having the form of a bulb bar structural memberwith bulb and flange portions, each said bulb portion being rectangularin cross section and each said flange portion being a flat planeextension of one side of the bulb portion, said flange portion beingsubstantially thinner in the transverse direction than the dimension ofthe rectangular bulb portion in its transverse dimension, each said bulbportion having a wood center core completely encased in a built up glassand plastic coating and each said flange portion being formed of thebuilt up glass and plastic per se to yield a stringer of high electricalinsulating value, said glass and plastic including a laminarconstruction of woven glass cloth and glass fiber matting with athermosetting polyester casting resin as a binder, there being plurallayers of said woven glass cloth in said flange and each such layerbeing continuous the length of the stringer to impart thereto a hightensile strength.

6. An extensible section for an insulator ladder, comprising a pair ofelongated parallel stringers defining side rails and carrying aplurality of parallel lateral rungs therebetween, each of said stringershaving the form of a bulb bar structural member with the bulb portionbeing rectangular in cross section and the flange portion being a flatplane extension of one side of the bulb portion, each said bulb portionhaving a Wood center core encased in a built up glass and plasticcoating and each said flange portion being formed of the built up glassand plastic per se to yield a stringer of high electrical insulatingvalue, said lateral rungs being spaced and therefore insulated one fromanother and being secured to said side rails by bolt means passingthrough and exerting a lateral compressive force upon said bulbportions, at least one of said wood center cores having two separatehalves comprising elongated pieces of wood arranged to abut and fittogether along the longitudinal centerline of the stringer, and a hollowlongitudinal tunnel piercing said latter wood center core to define acable way lengthwise through the stringer protected by said insulatedcoating.

7. In an extensible section of insulated ladder, an elongated continuousstringer defining one side rail of said ladder, said stringer having acenter core which is encased in a glass and plastic coating, saidcoating extending and projecting out from said core in a plane parallelthe longitudinal dimension of said stringer to form the flange portionof a structural member having the approximate form of a bulb bar havinga cross-sectional shape consisting of a rectangle and an outwardlyprojecting flange substantially narrower ill thickness than thethickness of the rectangle and consisting substantially of an extensionof one side face of the rectangle, the coating encasing said core anddefining said flange being formed of multiple layers of woven glasscloth and glass fiber matting with a thermosetting polyester castingresin as a binder to yield a high electrical insulating value andtensile strength.

8. In an extensible ladder for use by utility crews, an elongatedcontinuous stringer defining one side rail of said ladder, said stringerincluding a wood center core 10 encased in a built up glass and plasticcoating having a high electrical insulating value, said coatingextending and projecting out from said core in a plane parallel thelongitudinal dimension of said stringer to form the flange portion of astructural member having the approximate form of a bulb bar having across-sectional shape consisting of a rectangle and an outwardlyprojecting flange substantially narrower in thickness than the thicknessof the rectangle and consisting substantially of an extension of oneside face of the rectangle, the coating encasing said core and definingsaid flange being formed of Woven glass cloth and glass fiber mattingwith a thermosetting polyester castlng resin as a binder, the wovenglass cloth in said flange extending continuously without break thelength of the flange to impart thereto a high tensile strength.

9. An aerial ladder comprising an upright standard, a ladder including apair of elongate parallel stringers, means pivotally mounting saidstringers at the lower ends thereof upon the upper end of said standardfor pivotal movement about a horizontal axis, motor means for etfectingpivotal movement of said ladder about said axis comprising a cylindersecured at one end thereof to the lowerend of said standard for pivotalmovement about an axis parallel to said first mentioned axis, a pistonin said cylinder extending outwardly of the end of said cylinderopposite said one end, an elongate rigid sleeve slidably mounted on saidcylinder, a cross bar extending between and journaled to said stringersat a point spaced above the pivotal connection between said stringersand said standard, said cross bar being parallel to said axes, saidsleeve and said piston being rigidly secured to said cross bar, wherebyactuation of said motor effects pivoting of said ladder about themounting thereof upon said standard, and means to stabilize said ladderagainst lateral twisting comprising a pair of struts each engaging saidcross bar, one adjacent each of said stringers, said struts extendingfrom said cross bar angularly inwardly toward and being fixedly securedto the lower end of said sleeve.

10. An aerial ladder comprising an upright standard, a ladder includinga pair of elongate parallel stringers, means pivotally mounting saidstringers at the lower ends thereof upon the upper end of said standardfor pivotal movement about a horizontal axis, motor means for effectingpivotal movement of said ladder about said axis comprising a cylindersecured at one end thereof to the lower end of said standard for pivotalmovement about an axis parallel to said first mentioned axis, a pistonin said cylinder extending outwardly of the end of said cylinderopposite said one end, an elongate rigid sleeve slidably mounted on saidcylinder, a cross bar extending between and journaled to said stringersat a point spaced above the pivotal connection between said stringersand said standard, said cross bar being parallel to said axes, saidsleeve and said piston being rigidly secured at their upper ends to saidcross bar, whereby actuation of said motor effects pivoting of saidladder about the mounting thereof upon said standard, and means tostabilize said ladder against lateral twisting comprising a pair ofstruts each engaging said cross bar, one adjacent each of saidstringers, said struts extending from said cross bar angularly inwardlytoward and being fixedly secured to the lower end of said sleeve, and apair of brace members extending one between each of said struts and saidsleeve adjacent the upper end of the latter, said members being fixedlysecured to said sleeve and struts to retain the corresponding ends ofsaid struts in fixed position relative to said sleeve.

11. A ladder, comprising lower and upper ladder sections extensible withrespect to one another, a pair of elongated parallel stringers definingthe side rails of said upper sections, each of said stringers having theform of a bulb bar structural member having a cross-sectional shapeconsisting of a rectangle and an outwardly projectassesses.

ing flange substantially narrower in thickness than the thickness of therectangle, said flange being substantially an extension of one side faceof the rectangle, and said lower ladder section including a pair ofelongated metal truss structures defining the lower section side railsand in which said upper section side rails slidably are mounted.

12. An aerial ladder, comprising a lower ladder section carrying anupper ladder section which is extensible with respect thereto, saidupper section including a pair of elongated parallel stringers definingside rails and carrying a plurality of parallel lateral rungstherebetween, each of said stringers having the form of a bulb barstructural member with the bulb portion being rectangular in crosssection and the flange portion being a flat plane extension of one sideof the bulb portion, said lower ladder section including a pair of siderails each of which comprises an elongated metal channel section inwhich one of said upper section stringers is mounted, and said uppersection bulb portions being guided for extension movement upon journaledroller wheels which are carried by said lower section channels and whichproject within the outline bounded by the legs of the channels.

References Cited in the file of this patent UNITED STATES PATENTS CoreOct. 5, 1875 Ornatowski Sept. 15, 1896 Kramer Nov. 20, 1928 Fox May 16,1933 Cowan et al Mar. 31, 1936 Havens Oct. 19, 1937 Troche July 8, 1941Miller Sept. 28, 1948 Gerli et al Mar. 14, 1950 Short Nov. 21, 1950Rodgers Oct. 30, 1951' Stem Nov. 4, 1952 Eitel Feb. 3, 1953 Humpal Oct.6, 1953 Harsch Jan. 19, 1954 Hukari Apr. 6, 1954 De Luca Dec. 20, 1955Hopfeld Jan. 1, 1957 Balogh Jan. 15, 1957

